U.S. patent application number 11/699014 was filed with the patent office on 2008-07-31 for logarithmic response digital pixel sensor and method of processing digital signal thereof.
This patent application is currently assigned to LITE-ON SEMICONDUCTOR CORPORATION. Invention is credited to Yu-Chen Sung, Ming-Chieh Tsou.
Application Number | 20080179499 11/699014 |
Document ID | / |
Family ID | 39666883 |
Filed Date | 2008-07-31 |
United States Patent
Application |
20080179499 |
Kind Code |
A1 |
Tsou; Ming-Chieh ; et
al. |
July 31, 2008 |
Logarithmic response digital pixel sensor and method of processing
digital signal thereof
Abstract
A logarithmic response digital pixel sensor comprises a linear
light detecting unit, an exponential producer, a counting unit, a
comparator and a memory unit. The logarithmic response digital
pixel sensor is used for detecting light via the linear light
detecting unit for producing a linear analogy detecting signal. The
exponential producer is used for providing an exponential reference
signal. The comparator is used for comparing the linear analogy
detecting signal with the exponential reference signal and
outputting a comparison result to the memory unit. The memory unit
is used for producing a logarithmic response digital signal by
processing the comparison result and a count reference signal
provided from the counting unit. Thereby, the present invention
improves upon the drawbacks of the traditional logarithmic response
analogy image sensor, and simplifies the design of the back image
sensor processing circuit.
Inventors: |
Tsou; Ming-Chieh; (Hsin-Tien
City, TW) ; Sung; Yu-Chen; (Hsin-Tien City,
TW) |
Correspondence
Address: |
ROSENBERG, KLEIN & LEE
3458 ELLICOTT CENTER DRIVE-SUITE 101
ELLICOTT CITY
MD
21043
US
|
Assignee: |
LITE-ON SEMICONDUCTOR
CORPORATION
|
Family ID: |
39666883 |
Appl. No.: |
11/699014 |
Filed: |
January 29, 2007 |
Current U.S.
Class: |
250/214L ;
348/E3.018 |
Current CPC
Class: |
H04N 5/35518
20130101 |
Class at
Publication: |
250/214.L |
International
Class: |
G01J 1/44 20060101
G01J001/44 |
Claims
1. A logarithmic response digital pixel sensor, comprising: a
linear light detecting unit, used for detecting light and producing
a linear analogy detecting signal; an exponential producer, used
for providing an exponential reference signal; a comparator, used
for receiving the linear analogy detecting signal and the
exponential reference signal, and outputting the result of
comparing the linear analogy detecting signal with the exponential
reference signal; a counting unit, connected to the exponential
producer, and providing a count reference signal; and a memory
unit, used for receiving the comparison result outputted from the
comparator and the count reference signal for producing a
logarithmic response digital signal.
2. The logarithmic response digital pixel sensor as claimed in
claim 1, further comprising an encoder installed between the
counting unit and the memory unit, used for encoding the
logarithmic response digital signal to store the logarithmic
response digital signal in the memory unit.
3. A processing signal method of a logarithmic response digital
pixel sensor, comprising steps of: detecting light and producing a
linear analogy detecting signal; providing an exponential reference
signal and a count reference signal; comparing the linear analogy
detecting signal with the exponential reference signal and
outputting a comparison result; and receiving the comparison result
and the count reference signal for producing a logarithmic response
digital signal.
4. The processing signal method of logarithmic response digital
pixel sensor as claimed in claim 3, wherein the linear analogy
detecting signal is produced from a linear light detecting
unit.
5. The processing signal method of logarithmic response digital
pixel sensor as claimed in claim 3, wherein the exponential
reference signal is produced from an exponential producer.
6. The processing signal method of logarithmic response digital
pixel sensor as claimed in claim 3, wherein the count reference
signal is provided by a counting unit.
7. The processing signal method of logarithmic response digital
pixel sensor as claimed in claim 3, wherein the logarithmic digital
signal is produced by a memory unit receiving and processing the
comparison result and the count reference signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of processing a
digital signal of logarithmic response image sensor, and more
particularly to a CMOS logarithmic response digital pixel sensor
and a method of processing digital signals thereof.
[0003] 2. Description of Related Art
[0004] Recently, CMOS image sensors have become commonly used in
image detecting applications because they have high Quantum
efficiency, low power dissipation, low readout noise, wide dynamic
range, and random access ability. CMOS image sensors can also link
to the CMOS process to reduce costs, so it has gradually replaced
CCDs (Charge coupled devices). In all kinds of CMOS image sensors,
a logarithmic response image sensor receives stronger illumination
intensity, and has a wide dynamic range (around 120 dB) Compared
with linear image sensors (with a dynamic range of around 60 dB)
the logarithmic response CMOS image sensors are more suitable for
being installed in a device that reads pictures or dynamic images
via a photoelectric element, for example, a scanner, a cell phone
with an image capturing apparatus, a mini-camera, or a monitor,
etc.
[0005] Referring to FIG. 1, which shows a circuit diagram of a
current amplification logarithmic response CMOS image sensor, the
current amplification logarithmic response CMOS image sensor is
comprised of NMOS transistors 101,102,103, and a photodiode 104.
The current amplification logarithmic response CMOS image sensor
connects to the highest voltage via the gate of the NMOS transistor
101. At this time, the voltage difference between the gate and the
source of the NMOS transistor 101 forms a logarithm relation with
the current on the drain of the NMOS transistor 101. Thereby, the
relation between the output voltage Vout and the illumination
intensity received by the photodiode 104 is also the logarithm
relation, therefore the current amplification logarithmic response
CMOS image sensor has a very wide dynamic range, and image contrast
is very strong.
[0006] However, when reading out the voltage of the current
amplification logarithmic response CMOS image sensor, the mismatch
between pixels is easily influenced by a process of variation that
causes the signals to become irregular because the NMOS transistor
101 must operate in the subthreshold operation area to output the
logarithmic response signal, and, moreover, the process of
manufacturing the current amplification logarithmic response CMOS
image sensor makes the threshold voltage mismatched. Moreover, the
current amplification logarithmic response CMOS image sensor lacks
an effective method of removing fixed-pattern noise.
[0007] Although the current amplification logarithmic response CMOS
image sensor is highly sensitive and can rapidly switch speeds, the
photocurrent produced by the photodiode 104 receiving a usual range
illumination is too small when it passes through the NMOS
transistor 101. This causes the output voltage Vout to be limited
to a very small voltage difference range (about 0.2 V.about.0.5 V).
When an analogy/digital converter recognizes a pixel signal, the
input voltage range of the current amplification logarithmic
response CMOS image sensor is 1V, if it is being converted by an 8
bit analogy/digital converter, the output voltage Vout of the
current amplification logarithmic response CMOS image sensor must
have 1/256V sensitivity. Therefore, the design of the
analogy/digital converter in the back of the current amplification
logarithmic response CMOS image sensor for recognizing an output
voltage Vout is more complicated and difficult to implement.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing shortcomings of the prior art, the
present invention uses a linear analogy detecting circuit to detect
light and compare an exponential reference signal with a linear
reference signal to implement the function of an logarithmic
response digital pixel sensor and solve the problem in the back of
an A/D converter.
[0009] The present invention provides a logarithmic response
digital pixel sensor comprising of a linear light detecting unit,
an exponential producer, a counting unit, a comparator, and a
memory unit. The logarithmic response digital pixel sensor first
uses the linear light detecting unit to detect light and then
produces a linear analogy detecting signal. The exponential
producer provides an exponential reference signal. The comparator
compares the linear analogy detecting signal with the exponential
reference signal and outputs a comparison result to the memory
unit. The memory unit produces a logarithmic response digital
signal by processing the comparison result and a count reference
signal provided by the counting unit.
[0010] Additionally, an encoder is used for encoding the
logarithmic response digital signal, therefore the logarithmic
response digital signal can be processed using a different encoding
type and stored in the memory unit.
[0011] The present invention provides a processing signal method
for a logarithmic response digital pixel sensor comprising the
steps of: detecting light and producing a linear analogy detecting
signal; providing a exponential reference signal and a count
reference signal; comparing the linear analogy detecting signal
with the exponential reference signal and outputting a comparison
result; and finally receiving the comparison result and the count
reference signal for producing a logarithmic response digital
signal.
[0012] To make it easier for our examiner to understand the
innovative features and technical content, we use a preferred
embodiment together with the attached drawings for the detailed
description of the invention, but it should be pointed out that the
attached drawings are provided for reference and description but
not for limiting the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a circuit diagram of a current amplification
logarithmic response CMOS image sensor;
[0014] FIG. 2 is a functional block diagram of a logarithmic
response digital pixel sensor in accordance with the present
invention;
[0015] FIG. 3 is a curved diagram of the linear analogy detecting
signal and the exponential reference signal;
[0016] FIG. 4 is a curved diagram of the logarithmic response
digital signal; and
[0017] FIG. 5 is a flow chart of a processing signal method of a
logarithmic response digital pixel sensor in accordance with the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] Referring to FIG. 2, which shows a functional block diagram
of a logarithmic response digital pixel sensor in accordance with
the present invention, the logarithmic response digital pixel
sensor comprises a linear light detecting unit 21, an exponential
producer 22, a comparator 23, a memory unit 24, a counting unit 25,
and an encoder 26. In order to improve upon the drawbacks of the
logarithmic response analogy image circuit detecting light signal,
the present invention uses the linear light detecting unit 21 to
detect a light signal for producing a linear analogy detecting
signal Sout. The exponential producer 22 provides an exponential
reference signal Eout, the counting unit 25 provides a count
reference signal. The linear analogy detecting signal Sout and the
exponential reference signal Eout are transmitted to the comparator
23 for comparing, and then the comparator 23 outputs a comparing
result to the memory unit 24. The memory unit 24 produces a
logarithmic response digital signal Dout, according to the
comparing result from the comparator 23 and the count reference
signal from the counting unit 25. Furthermore, the logarithmic
response digital signal Dout is stored in the memory unit 24 and
provides an application system 27 to read and process the signals.
Thereby, the design of the analogy/digital converter in the back of
the image sensor is uncomplicated and easily to implement.
[0019] The encoder 26 is installed between the counting unit 25 and
the memory unit 24, and encodes the logarithmic response digital
signal Dout to a required code, and then stores the encoded
logarithmic response digital signal Dout in the memory unit 24 for
the application system 27 to read and process.
[0020] Referring to FIG. 3, a curved diagram of the linear analogy
detecting signal and the exponential reference signal, the
illumination-output voltage curve of the linear analogy detecting
signal Sout and the exponential reference signal Eout is shown. The
linear analogy detecting signal Sout and the exponential reference
signal Eout are inputted to the comparator 23. The comparator 23
then outputs a comparing result to the memory unit 24 for producing
the digital logarithmic curve as shown in FIG. 4, a curved diagram
of the logarithmic response digital signal. The logarithmic
response digital pixel sensor of present invention thereby
implements the digital signal output and the logarithmic response
output, and improves upon the shortcomings of the prior art.
[0021] Please refer to FIG. 5, which is a flow chart of a
processing signal method for a logarithmic response digital pixel
sensor in accordance with the present invention. The linear light
detecting unit 21 first detects light for producing a linear
analogy detecting signal (shown in FIG. 5 as S501). Next, the
exponential producer 22 provides an exponential reference signal
for comparison with the linear analogy detecting signal, and the
counting unit 25 provides a count reference signal to the memory
unit 24 (shown in FIG. 5 as S503). Next, the comparator 23 compares
the linear analogy detecting signal with the exponential reference
signal and provides a comparing result to the memory unit 24 (shown
in FIG. 5 as S505). Finally, the memory unit 24 produces a
logarithmic response digital signal for the application system 27,
according to the comparing result outputted from the comparator 23
and the count reference signal provided from the counting unit 25,
thereby, the application system 27 can read the logarithmic
response digital signal from the memory unit 24 to operate and
process (showed as FIG. 5 S507).
[0022] In summation of the description above, the present invention
using the linear analogy detecting unit to detect light improves
upon the drawbacks of the prior art, and achieves the function of
the logarithmic response image sensor by comparing the linear
analogy detecting signal with the exponential reference signal, so
that the design of the analogy/digital converter in the back of the
image sensor will be uncomplicated and easily to implement. The
signal process of the logarithmic response digital pixel sensor of
the present invention has the advantage of low power consumption,
fast operating speed and low production costs, so that the
logarithmic response digital pixel sensor of the present invention
can be integrated into a SOC system easily and with successful
results.
[0023] Although the present invention has been described with
reference to the preferred embodiments thereof, it will be
understood that the invention is not limited to the details
thereof. Various substitutions and modifications have been
suggested in the foregoing description, and others will occur to
those of ordinary skill in the art. Therefore, all such
substitutions and modifications are intended to be embraced within
the scope of the invention as defined in the appended claims.
* * * * *